Fuse resistor and the method for making same

ABSTRACT

A fuse resistor is comprised of a wire resistor adapted to fuse and break in response to a predetermined magnitude of current passing therethrough. A silicone rubber casting surrounds the wire resistor. The wire resistor and the silicone rubber coating are embedded within a dielectric body member, and electrical contact means are connected to the resistor and extend outside the body member. The body member can be a disc which is adapted to be inserted within a light bulb socket between the light bulb and the terminals of the socket. The method of the present invention comprises coating a wirewound resistor with a silicone rubber, and molding the wire-wound resistor within an electrically insulative material so that the resistor is embedded within the insulative material with only its terminals protruding outwardly therefrom.

United State s Patent 1191 Kreifels 1451. Feb. 12, 1974 [22] Filed:

[ 1 FUSE RESISTOR AND THE METHOD FOR MAKING SAME [75] Inventor: Clifford A. Kre fels, Columbus,

Nebr.

[73] Assignee: Dale Electronics, Inc., Columbus,

Nebr.

Nov. 26, 1971 21 Appl. No.: 202,307

[52] U.S. Cl 337/163, 337/160, 337/296, 338/266 [51] Int. Cl. H0lh 85/14 [58] Field of Search... 337/160, 163, 166, 246, 290, 337/296, 187, 276, 107, 266; 174/52 PE [56] References Cited Fisher 337/163 X [57 1 ABSTRACT A fuse resistor is comprised of a wire resistor adapted to fuse and break in response to a predetermined magnitude of current passing therethrough. A silicone rubber casting surrounds the wire resistor. The wire resistor and the silicone rubber coating are embedded within a dielectric body member, and electrical contact means are connected to the resistor and extend outside the body member. The body member can be a disc which is adapted to be inserted within a light bulb socket between the light bulb and the terminals of the socket. The method of the present invention comprises coating 3 wirewound resistor with a silicone rubber, and molding the wire-wound resistor within an electrically insulative material so that the resistor is embedded within the insulative material with only its terminals protruding outwardly therefrom.

9 Claims, 5 Drawing Figures FUSE RESISTOR AND THE METHOD FOR MAKING SAME This invention relates to a fuse resistor and a method for making same.

Fuse resistors are often very valuable in electronic circuits for the purpose of preventing damage to electrical components within the circuit in the event of shorting out in other components within the circuit. For example, in a circuit including a light bulb and a plurality of solid state components, damage can be done to the solid state components if the filament of the light bulb shorts out and reduces the resistance within the circuit. Often when a light bulb burns out, the filament momentarily short circuits and causes impulses of current to be sent through the circuit. Such impulses can often damage the other components within the circuit. Fuse resistors, if placed in the circuit in series with the light bulb, can protect the other components of the circuit against such impulses. When the light bulb shorts out the impulse of current causes the fuse resistor to break the circuit thereby protecting the other components in the circuit from surges of current.

One disadvantage of providing a fuse resistor which is permanently connected in the circuit, however, is that the fuse must be replaced in the event it burns out. In the light bulb illustration referred to above, the fuse resistor may burn out simultaneously with the burning out of the light bulb. The present invention contemplates solving this problem by providing a fuse resistor which can be inserted in the socket of the light bulb between the light bulb and the terminals of the socket. Such a fuse resistor could be replaced easily at the time that the light bulb is replaced.

In order to provide such a fuse resistor, it is desirable to embed the fuse resistor within a dielectric material so that a wafer or disc is formed with the fuse resistor embedded therein. Ordinary wire-wound resistors have wire surrounded by compound which holds the wire in place. When such resistors are embedded in dielectric materials such as epoxies, the wire is held in place when it fuses, and this often prevents clean fusing. Often the compound surrounding the fuse resistor is burned until it builds up enough pressure to crack or explode the unit.

The present invention has solved this problem by providing a silicone rubber coating around the wirewound resistor, and then embedding the silicone rubber coating and the resistor within a dielectric material formed in the desired shape. The silicone rubber coating permits the resistor to fuse and break the circuit cleanly without any burning of the compound and without creating pressure which might crack or explode the unit.

Therefore a principal object of the present invention is the provision of a fuse resistor which can protect electrical components within a circuit from undesirable magnitude or surges of current.

A further object of the present invention is the provision of a fuse resistor which can be embedded within an epoxy, silicone, or other dielectric material.

A further object of the present invention is the provision of a device which will fuse properly even though embedded in a dielectric material.

A further object of the present invention is the provision of a device which can be fitted within a light bulb socket, or which can be embedded within a material so as to assume any molded desired shape.

A further object of the present invention is the provision of a device which can be replaced merely by removing a light bulb from the socket.

A further object of the present invention is the provision of a device which can be manufactured by a molding process wherein a fuse resistor is molded within a dielectric material.

A further object of the present invention is the provision of a device which will protect other components in a circuit from surges of electric current resulting when a light bulb in the circuit burns out.

A further object of the present invention is the provision of a device which will minimize a surge of current in the circuit resulting when the circuit is initially actuated.

A further object of the present invention is the provision of a device which is economical to manufacture and is dependable in use.

These and other objects will be apparent to those skilled in the art.

This invention consists in the construction, arrangements and combination of the various parts of the device, whereby the objects contemplated are attained as hereinafter more fully set forth, specifically pointed out in the claims, and illustrated in the accompanying drawings in which:

FIG. 1 is a partial sectional view of a light bulb socket utilizing the fuse resistor of the present invention.

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a sectional FIG. 2.

FIG. 4 is an enlarged sectional view taken along line 4-4 of FIG. 3.

FIG. 5 is a schematic view showing the resistor in series with the light bulb.

Referring to FIG. 1, a light bulb includes a glass filament chamber 12 and a threaded end 14. Threaded end 14 is comprised of a metallic electrical conducting material. A center contact 16 is provided at the extreme lower end of bulb 10, and is mounted in conventional fashion within threaded end 14 so that it is insulated from the metallic casing of threaded end 14. Within chamber 12 is a filament 18 which is in electrical contact with center contact 16 and with the metallic casing of threaded end 14. All of the above construction is conventional for light bulbs.

A conventional socket 20 includes a dielectric socket body 22 and an annular metal casing 24 having threads therein for receiving threaded ends 14 of bulb 10. At the bottom of socket 20 is a center terminal 26. Center terminal 26 and annular casing 24 provide a pair of terminals which normally are adpated to contact center contact 16 and threaded end 14 of bulb 10. Normally the resulting circuit would be through center terminal 26, center contact 16, filament l8, and threaded end 14 to annular metal casing 24. All of the above is conventional in the art of light bulbs.

The present invention differs from conventional structure, however, in that a disc fuse resistor 32 is interposed between center terminal 26 of socket 20 and center contact 16 of bulb 10. The fuse resistor 32 includes a dielectric wafer or disc 34 which is approximately circular in shape so as to conform to the interior of socket 20. A pair of notches 36 are formed in the opposite margins of wafer 34. Embedded within wafer 34 is a wire-wound resistor 38 having a wire coil 40 which view taken along line 33 of surrounds a ceramic or other dielectric core 42. At the opposite ends of coil 40 are two metal caps 44 which include leads 46 extending therefrom and which provide electrical terminals at the opposite ends of coil 40. Caps 44 are secured over the opposite ends of core 42, and the opposite ends of coil 40 are welded to caps 44 so as to insure solid connection therebetween. Welded to leads 46 are an upper tab 48 and a lower tab 50. Upper tab 48 extends above and outwardly of wafer 34, and lower tab 50 extends below and outwardly of wafer 34.

A silicone rubber material 52 surrounds wire coil 40 and coats the wires within coil 40 and the outer edges of caps 44. The type of material 52 which surrounds coil 40 is important to the satisfactory operation of the present invention. Ordinary wire-wound resistors include wire coils surrounded by materials which actually hinder fusing. These materials hold the molten wire in place and prevent clean fusing until the wire has burned enough of the surrounding compound away to allow it to part and open the circuit. By this time the unit may have cracked or exploded or burst into flames. Even after such resistors fuse there is often a conductive path left by the burned organic materials in the encapsulation. This can provide a high resistance path and thereby prevent a true open circuit.

Thus the material 52 to be used with the present invention must have the following properties:

1. It must be soft and flexible so as to allow the wire some freedom to pull apart when melted by fuse action currents.

2. It must rapidly deteriorate at the fusing temperatures of the wire (approximately l,200 C), thus giving the wire additional room to part.

- 3. It must create a minimum of outgassing and conductive residues under the above conditions.

4. It must act as an arc quenching agent to cause clean sharp fusing and to prevent restrikes.

5. It must be capable of being used as a first coat over the coil and then be encapsulated within normal resistor coating materials for environmental protection.

All of the above properties are achieved through the use of a silicone rubber coating over the wire. The units are then molded using normal silicone or epoxy molding compounds. This gives the protection, durability, and appearance of a normal molded resistor, while allowing the wire to fuse almost as readily as with no coating at all.

A number of different silicone rubber compounds have been used successfully. Examples are silicone rubber manufactured by Dow Corning designated No. 732 RTV and by General Electric designated Nos. 1 l2 RTV and 630 RTV. Apparently, any silicone rubber will suffice in the present application.

Disc fuse resistor 32 is inserted within socket 20 between bulb and the lower end of socket 20. Upper tab 48 is in engagement with center contact 16 of bulb l0, and lower tab 50 is in contact with center terminal 26 of socket 20. The resulting configuration provides a circuit with wire-wound resistor 38 and filament 18 in series connection with one another. Other electrical components may be connected in the circuit with resistor 38 and filament 18, but these components are not shown in the drawings.

Disc fuse resistor 32 provides a valuable function in the circuit as shown. When light bulb 10 is initially turned on, filament 18 is cold, and therefore its resistance is low. Thus, initially there is a surge of current within the circuit which is caused by the low resistance in filament 18. This momentary surge in current is dampened by resistor 38, and therefore prevents damage to the other components within the circuit. In the event that filament l8 burns out, there is a danger that the filament may, at least momentarily, short out and also cause pulses of increased current to be realized in the circuit. In the event that a pulse of current occurs which exceeds a predetermined rated value of resistor 38, resistor 38 fuses and breaks the circuit so as to prevent any further shorting out thereof. The silicone rubber provides a valuable function in this regard. Most other compounds surrounding a wire-wound resistor hold the molten wire in place when the resistor is fusing. This can prevent the clean breaking of the circuit and can cause restrikes and burning of the compound surrounding the resistor until sufficient pressure is built to crack or explode the entire unit. Silicone rubber coatings over the wire permit the unit to be molded within a dielectric material and still fuse properly without the problem referred to above.

In making the resistor of the present invention, wirewound resistor 38 is constructed in conventional manner. Silicone rubber coating 52 is then applied over coil 40 and the outer edges of caps 44. Then the entire wirewound resistor 38 with silicone rubber coating 52 thereon is molded and embedded within a dielectric material such as epoxy resin to provide the-desired shape. The epoxy resin may be molded into any shape desired, as for example, the wafer shape shown in the drawings.

Instead of using the molding process, as referred to above, the wire-wound resistor 38 could be inserted within stamped dielectric members and secured therein. This would be accomplished more in the nature of packaging the resistor within a member having the desired configuration.

While disc fuse resistor 32 is shown in the drawings to be entirely separate from bulb 10, it is also possible to make this resistor an integral part of bulb 10. The molding process referred to above, would permit resistor 38 to be molded within any shape which could be inserted or made an integral part of bulb 10.

Thus it can be seen that the device accomplishes at least all of its stated objectives.

I claim:

1. A fuse resistor comprising:

a wire resistor adapted to fuse and break in response to a predetermined magnitude of current passing therethrough;

a silicone rubber coating surrounding said wire resistor;

a body member comprised of an electrically insulative material;

said wire resistor and said silicone rubber coating being embedded within said body member, said wire resistor being separated from direct contact with said body member by said rubber coating; and

Electrical contact means connected to said resistor and extending outside said body member.

2. A fuse resistor according to claim 1 wherein said wire resistor is a wire-wound resistor having a coil of wire wound around a core of electrically insulative material.

3. A fuse resistor according to claim 1 wherein said body member is a substantially circular disc having upper and lower surfaces, said contact means including one contact member extending from said upper surface and one contact member extending from said lower surface.

4. A fuse resistor according to claim 1 wherein said body member is molded from an epoxy material.

5. A method for making a fuse resistor comprising: coating a wire-wound resistor having terminals with a silicone rubber material so that the wire of said wire-wound resistor is surrounded by rubber silicone;' molding said wire-wound resistor within an electrically insulative material, said wire resistor being separated from direct contact with said insulative material by said silicone rubber material so that said resistor is embedded within said insulative material with only its terminals protruding outwardly therefrom. 6. In combination: a light bulb socket having a pair of terminals; means for providing voltage across said terminals; a light bulb filament; a fuse resistor, said fuse resistor being connected in series with said light bulb filament, across said terminals; and I said fuse resistor being adapted to fuse and break the circuit between said terminals and said filament in response to passage of current of a predetermined magnitude through said fuse resistor said fuse resistor comprising a wire, resistor surrounded by a silicone rubber coating and embedded within an electrical insulating material, the wire being separated from direct contact with said insulating material by said silicone rubber coating.

7. A combination according to claim 6 wherein said filament is within a light bulb having a portion thereof matingly fitted within said socket, said fuse resistor also being within said socket.

8. A combination according to claim 7 wherein said fuse resistor is positioned between at least one of said terminals and said portion of said light bulb within said socket.

9. A combination according to claim 8 wherein said bulb includes a pair of contacts connected to said filament, said fuse resistor also having a pair of contacts, one of said resistors contacts engaging one of said terof said bulbs contacts.

contacts engaging one 

1. A fuse resistor comprising: a wire resistor adapted to fuse and break in response to a predetermined magnitude of current passing therethrough; a silicone rubber coating surrounding said wire resistor; a body member comprised of an electrically insulative material; said wire resistor and said silicone rubber coating being embedded within said body member, said wire resistor being separated from direct contact with said body member by said rubber coating; and Electrical contact means connected to said resistor and extending outside said body member.
 2. A fuse resistor according to claim 1 wherein said wire resistor is a wire-wound resistor having a coil of wire wound around a core of electrically insulative material.
 3. A fuse resistor according to claim 1 wherein said body member is a substantially circular disc having upper and lower surfaces, said contact means including one contact member extending from said upper surface and one contact member extending from said lower surface.
 4. A fuse resistor according to claim 1 wherein said body member is molded from an epoxy material.
 5. A method for making a fuse resistor comprising: coating a wire-wound resistor having terminals with a silicone rubber material so that the wire of said wire-wound resistor is surrounded by rubber silicone; molding said wire-wound resistor within an electrically insulative material, said wire resistor being separated from direct contact with said insulative material by said silicone rubber material so that said resistor is embedded within said insulative material with only its terminals protruding outwardly therefrom.
 6. In combination: a light bulb socket having a pair of terminals; means for providing voltage across said terminals; a light bulb filament; a fuse resistor, said fuse resistor being connected in series with said light buLb filament, across said terminals; and said fuse resistor being adapted to fuse and break the circuit between said terminals and said filament in response to passage of current of a predetermined magnitude through said fuse resistor said fuse resistor comprising a wire resistor surrounded by a silicone rubber coating and embedded within an electrical insulating material, the wire being separated from direct contact with said insulating material by said silicone rubber coating.
 7. A combination according to claim 6 wherein said filament is within a light bulb having a portion thereof matingly fitted within said socket, said fuse resistor also being within said socket.
 8. A combination according to claim 7 wherein said fuse resistor is positioned between at least one of said terminals and said portion of said light bulb within said socket.
 9. A combination according to claim 8 wherein said bulb includes a pair of contacts connected to said filament, said fuse resistor also having a pair of contacts, one of said resistor''s contacts engaging one of said terminals of said socket and the other of said resistor''s contacts engaging one of said bulb''s contacts. 